Signal transduction: Gyrating protein kinases Jeff Stock  Current Biology  Volume 9, Issue 10, Pages R364-R367 (May 1999) DOI: 10.1016/S0960-9822(99)80228-0

Figure 1 Two-component histidine–aspartate phosphorelay systems mediate signal transduction in microorganisms and plants. The mechanism generally involves autophosphorylation of a specific histidine residue within a histidine kinase, and subsequent transfer of the phosphate to a specific aspartate residue in the receiver domain of a cognate response regulator. Current Biology 1999 9, R364-R367DOI: (10.1016/S0960-9822(99)80228-0)

Figure 2 The conserved histidine kinase catalytic core is composed of a dimerization domain of two up-down α helices, each connected at its carboxyl terminus to an independent ATP/ADP-binding phosphotransfer domain. The phosphotransfer domain of each subunit generally catalyzes the phosphorylation of a histidine residue within the amino-terminal dimerization helix of the opposing subunit. Current Biology 1999 9, R364-R367DOI: (10.1016/S0960-9822(99)80228-0)

Figure 3 Structural organization of CheA. The protein is a dimer, with each subunit composed of an amino-terminal four-helix bundle (H domain) attached to a domain (YB) that binds the chemotaxis response regulators CheY and CheB. Following the YB domain is the histidine kinase catalytic core, composed of dimerization and ATP-binding domains (see Figure 2). Tandem SH3 domains at the carboxyl terminus of CheA mediate the assembly of receptor signaling complexes. CheA differs from most histidine kinases in that the site of histidine phosphorylation is located within a distinct amino-terminal four-helix bundle, rather than in the amino-terminal helix of the dimerization domain. Nevertheless, phosphorylation occurs in trans with the ATP-binding domain of one subunit phosphorylating the H domain of the other subunit. Current Biology 1999 9, R364-R367DOI: (10.1016/S0960-9822(99)80228-0)